True enough but bronze tender was the paper money of the time. It took ages to convince the civilized world that a promise of value equaled actual value.
The barbarian mercenaries the latter day Romans came to depend on for their national security demanded gold or plunder and they cared not where it came from.
Bronze does not bend easily when bitten and the savages would not be cheated.
:’) There was practically no gold paid to the legions and auxiliaries over the centuries of the Roman Empire, and the bigger the empire got, the more currency was needed. Soldiers were paid in salt (that’s where the word “salary” comes from), vinegar, room and board, and after action booty from the occasional vanquished enemy. Bronze coin was never treated as paper money where gold could be demanded.
Trajan’s big gold strike came from his conquest of Dacia with its gold mines, which go back into prehistory a bit; Trajan’s catamite-loving successor had to be talked into hanging on to Dacia, but retreated from other areas (most famously, building Hadrian’s Wall), and spent his time as emperor travelling a good bit of the Empire, and persecuting the Jews, all the while knocking off young boys.
Rome’s gold supply went off into trade with India, if the complaints of at least one surviving Roman writer is true. The figures of this flow of gold were exaggerated (at best). Gold is rarely found on ancient wrecks from any era, it just wasn’t carried along as a rule; trade was in goods, iow barter.
OTOH, some enterprising Roman actually brought pottery makers from India and established their industry on the Egyptian shore of the Red Sea, thus moving the supply closer to the Roman market, and obviating the need for the time factor of the monsoon trade route. Rome learned of the orangutan and brought it as a curiousity to amuse the riff raff, and imported a lot of pepper, not to mention the silk and other common Far East goods.
The Byzantines controlled a buttload of trade thanks to the location, and of course, they persisted a long time, so gold Byzantine coins are fairly commonplace today. A good many of the bronze coins dug up in the Balkans by people armed only with metal detectors are of late Roman Empire date, but a good many are Byzantine.
Byzantine goods were traded by sea throughout the former Roman west, as pottery (which persists even in a broken state for a long time in the soil) and other stuff from Byzantium is found in archaological contexts in the UK. I suspect that any coin in use in post-Roman Britain was locally circulated, and that commercial transactions were by barter, which always works.